87 

 Gen. 24. Idya, Philippi, 1843. 



83^11: Thisbe, Lilljeborg. 



Generic Characters. Body more or less distinctly depressed, with the 

 anterior and posterior divisions sharply defined. Cephalic segment of moderate 

 size and narrowly produced in front, rostral projection short and obtuse, not de- 

 fined at the base. Epimeral plates of the 3 succeeding segments rather broad, 

 lamellar, obtuse at the tips. Last segment of metasome very small. Urosorae 

 moderately slender, with the genital segment in female more or less distinctly 

 divided in the middle, genital tubercles in male each armed with a strong 

 posteriorly-pointing spine. Caudal rami generally short but, with some of the 

 apical setse much elongated. Eye normal. Anterior antennae more or less slender 

 and attenuated, 8-articulate, sensory filament of 4th joint very fully developed; 

 those of male slightly transformed, subprehensile. Posterior antennae with the 

 outer ramus well developed, 4-articulate. Anterior lip rather prominent, tapering 

 clistally, terminal edge minutely denticulate. Mandibles with the masticatory part 

 rather slender and coarsely dentated at the tip, palp of comparatively simple 

 structure, though distinctly biramous. Maxillse with the palp only very slightly 

 lobular, epipodal lobe wholly absent. Both pairs of maxillipeds uncinate at the 

 tip, the anterior ones biarticulate, with a single very slender lateral lobe at the 

 junction of the two joints, the posterior ones distinctly 3-articulate, with a single 

 slender apical claw. First pair of legs with both rami 3-articulate, but rather 

 unequal in size and structure, the inner one much longer than the outer and 

 having the penultimate joint more or less prolonged, the last very small with 2 

 comparatively short claws; outer ramus with the spine of the 1st joint, as a rule, 

 much elongated, that of 2nd joint issuing from near the end, last joint provided 

 at the inner corner with 2 slender ciliated setae, and along the obliquely trun- 

 cated end with 4 outward-curving spines gradually increasing in length, and each, 

 like that of the 2nd joint, penicillate at the tip, or clothed on one edge with a 

 limited number of long cilia. Natatory legs comparatively largely developed, with 

 the rami nearly equal and the joints rather broad sublamellar; middle joint of inner 

 ramus in all pairs with 2 natatory setse. Last pair of legs more or less slender, 

 extended laterally, proximal joint only very slightly 'expanded inside, distal joint 

 generally narrow, linear; those in male not very different, though somewhat 

 smaller than in female. 



Semarks. This genus was established in the year 1843 by Philippi, to 

 include a Mediterranean species, I. barbigera Phil. Prof. Lilljeborg did not recog- 

 nise the Philippian genus, and established a new genus, Tlrisbe, for the reception 



